[Scenario] Expose end time in Activity

Info view now supports interdependent extended property fields,
so end time can be shown alongside duration and start time.
[Scenario] Simplify time property editors, add to decision

Consolidated different property editors for time (start, end, duration)
into one class. Also added these editors to decision.
[Scenario] Remove obsolete property editors
[Scenario] Merge changes to utilize InfoView's auto-refresh

InfoView auto-refreshes as of nasa/mct#153. This allows the
completion of nasa/MCT-Plugins#9, whereby the info view for
activities and decisions should contain all three of start time,
end time, and duration. Previously end time had been suppressed
because it was not possible to stay "in sync" with the other
values (to satisfy the expectation that duration=end-start) in
the visible GUI, even though appropriate adjustments were made
in the model. With InfoView's refresh upon change, these
adjustments are reflected to the user.